Relationship between pain, elbow valgus instability, and the function of flexor pronator muscles in baseball players

We hypothesize that ulnohumeral joint space distance due to gravity valgus stress may not be related to pain in the medial elbow of the dominant arm in baseball players.

Thirty-one male baseball players were divided into an ulnar collateral ligament (UCL) injury group (n = 16) and a Healthy group (n = 15). The injury groups were diagnosed with UCL injury by magnetic resonance imaging, and was defined as having pain during throwing. The medial elbow of each player's throwing arm was imaged by ultrasonography under valgus stress. The ulnohumeral joint space was measured for horizontal and vertical distances. The examiner added resistance force on the subject in order to produce isometric contraction of the forearm pronator muscles (FPMs). Measurements were taken at rest and at FPM isometric contraction. The Mann-Whitney U test was used to compare data between the dominant and nondominant sides, and between the UCL injury group and the Healthy group.

The horizontal and vertical distance at rest on the dominant side was not significantly different between 2 groups. The vertical distance during contraction of the flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), and pronator teres (PT) muscles was significantly different between the UCL injury group and the Healthy group (P < .05) and was shifted laterally. A shift in the lateral direction indicates an increase in valgus instability.

The dominant side suggested that the space in the ulnohumeral joint space was wider, with or without pain. It was suggested that players with medial elbow pain may have impaired FCR, FCU, and PT function.